Physicist Carlo Rovelli has a nice short book called "Order of Time" where he explains this quite vividly. Basically "now" is only applicable to "here" and we intuitively extend it to things around, and that kind of works while discrepancies remain too small to notice. But on a larger scale "now" doesn't mean what we're used to, it loses its meaning. All the region of spacetime outside our past and future light cones is "extended present" with no fixed order "before or after or now" relative to us, and it's not directly observable anyway. He offers some casual metaphors from real life to get accustomed to such thinking.
@@Mahesh_Shenoy How do you know that we don't see Andromeda galaxy as it is right now? Relativity of simultaneity means you cannot agree on what is right now outside your reference frame therefore you cannot claim that light takes time to travel towards you because that is only under the assumption that light travel at speed of light in every direction. The truth is two way speed of light is constant but the light could travel one way at any speed between c/2 and infinity.
@@classicalmechanic8914that's why Einstein already mentioned in his original 1905 paper about light Speed. He said that "all the theory is made under the speculation about TWO WAY LIGHT SPEED is 'c'. We never know one way light speed. So one way light speed can be even infinite, but there is no way to test it. So we kind of belive it that it is c/2. Because we can't even test it or prove it nor disprove it.
And nobody knows what the spacelike 'extended present' outside of our light cone means. It is interesting, as this is where inflation and all cosmic theories come in, considering the cosmic background radiation is within our (past) light cone. We have no idea or even an inklinkg what this spacelike extended present could even mean. Now that I mention this, I wonder what the implications for black holes are, where apparently time and space kind of switch, this means there is a phase transition in what it means to be an spacelike extended present. Wonder what it could tell us about it, the black hole dynamics. Considering our current universe would be the spacelike extended present for the black hole at the event horizon where time and space switch roles and flip!
@@classicalmechanic8914It should be possible to see Andromeda (thougj may not be probable) at it is in the present or by a margin of a few seconds (also taking into account delay in our consciousness of reality). That is, thru a wormhole. But if there are naturally more wormholes in the universe, well, we could have been seeing things that are much farther away than they really are, and we are there seeing a mixed of observation of the past in the present.
That was the smoothest segue of introducing a sponsor into a UA-cam video that I have ever seen. Einstein was asked if a femtosecond is the shortest measurement of time. He answered no. The shortest measurement of time is the time between when a traffic light in New York City turns green and when the driver of the car behind you beeps his horn.
It is astounding how you've managed to clear up EVERY single follow up question i had after watching your earlier videos (coming in from the triplet paradox video). In three videos you have cleared up questions I've had unanswered for years. You should be required viewing in every science class in every school, anywhere. This is a level of teaching excellence that I've not only never seen before, but never even thought possible.
If the universe is moving forward and you move forward with the universe, did you really move forward yourself? If I were on Mars at 9 o:clock what time would it be here on Earth? It wouldn't relate. The orbit of Mars is not equal to the orbit of Earth so the hours in the day would not even be close. If 1 day of Earth was 3 months of Mars how much older would I be when I get to mars and do I age the same as if I were on Earth? I would age the exact same on either planet of Galaxy. We are moving forward with the universe.
This video is some truth and a lot of rubbish. Ppl love to talk like they know about things they just don’t know. There’s sooooo much we just don’t know or understand. Keep seeking TRUTH. Only Our Creator actually knows what’s up. Seek Him. 🙏
Mahesh, all the hard work in the animations and the smooth delivery of explanations are revolutionary and all, but deep down you know you've turned pro when you've seamlessly segue into the sponsor spot without any transition. Achievement unlocked! Einstein says he is proud. It's ok if you didn't hear it, he was in another frame 😉
To address the very last question in the video You explain it very well and ill put it in different words: Someone once explained it to me in a very simple way - each observer: me, the jogger and the aliens in Andromeda have their own time. Imagine it like a track, and the word "now" is a point on that track. Since every one has their own track, the word "now" is personal. Ie each person's now will refer to a point along his own tracks - there is no necessity to be able to map each point on your tracks to some point on another's (arbitrary) tracks. They are simply just different tracks, and each observer has chosen a different path through spacetime. You dont have to be able to link these tracks together, why would you?
@@MadsterV no it's meaningless to speak about its time in a way that maps points on its time to ours unless that meteor is local which it will be long before it hits us. It's like hearing someone say "the *local* speed of light is c" and then saying "oh so the speed of light isn't constant, they lied to us" And anyway - the meteor hitting us is an absolute truth, it either hits us or doesn't. So we can use *our* time to track it - nobody is forcing us to link our time to the meteor's time. And anyway (again) if we want to predict what state it will be in by the time it hits us (eg idk, perhaps what percentage of its radioactive isotopes will have undergone fission), yes we can use its own time - again, linking it to ours is unnecessary for this calculation
I'm taking a bunch of classes right now online, in unrelated subjects, and I just want all of those instructors to watch your videos. A good teacher makes such a difference!
Andromeda is not just separated from us in space but also equally in time. Just as we can not reach Andromeda in space, we can not reach it in time. We're essentially de-synced in time by 2.5 million years. If we were to travel to Andromeda, that desync in time would shrink as the distance between us shrank. So when we arrive somewhere we don't just arrive there in space, but also in time. Hence the term, spacetime. With that in mind, the "present" is only local to you, and the further something is from you the more in the past it is from you as well.
That's a great point. Weirdly, our human brains deals as "there is an universal clock, now is happening everywhere, and when we see the stars, the light travelling to us gives an illusion that something is happening right now" But it's false. It's not an illusion. The real "now" is the speed of light. "Seeing the past" is not an illusion, is the real "now" for you locally
Which would make it really cool to watch it as we traveled toward it to see what happens all the way up to the point where we reach it and see it as it is at that point.
unfortunately your statement, however clever, is still not quite right. it assumes there's an absolute set of 4 dimensional coordinates, three spatial and one time, but that's not quite the case. in reality, we have local sets of 4 dimensional coordinates (our frames of reference) but their relation to other frames of reference change as a function of of many dynamic variables, it's not as simple as setting a desired point in 4-dimensional world and then saying we'll meet there, the "there" changes as the world and you evolve
No. If you could hop in a wormhole you’d be at andromeda now. Yes what we see now is them 2.5 million years ago. But it does exist in the now. We just can’t see it now cause its light is taking time to get here.
This is why it's good to play with simulators that use a speed of light much slower than normal, so one can develop a better feel for how "now" is relative.
Speed has nothing to do with forward motion. You can go forward at 1 mph. Everything inside of you is only going 1 mph. Nothing inside of you will go faster or slower than you are.
This is the first video that's convinced me that faster-than-light travel is impossible, as it would create causal paradoxes: Lets say we have three FTL communicators, two nearby (B & C), and one in Andromeda (A). Lets say B and C are nearby, but C is jogging. B says to A "tell C to tell me to say 42", then A tells C that, but C will hear that message days before B sent it, so can tell B not to send any message at all, creating a paradox.
That’s not how it works, C will hear the message days before they would be able to observe B sending it but C’s observation of B sending it is irrelevant to affecting wether or not B did send it I swear these misunderstandings are only possible because we’re taught a very self centred version of time. Going faster than the speed of light is not time travel otherwise we already have that with sound you can just go further away faster than the speed of sound and hear what happened earlier than your previous observation but if you were going slower than the speed of light you won’t be seeing before your previous observation. Only difference in your example is now light is the one coming in second place. Edit: I said the same thing twice
I never understood why people believe that faster than light is impossible because otherwise you could get a message before you observe someone sending it... Or that you could meet an alien before you saw them leave their home planet or whatever else. Like none of that means FTL is impossible and isnt at all odd to think about even, nor is it timetravel. Just because you travel say 2c doesnt mean you can affect the past by sending a message somewhere and them being able to send a response before you sent your message. Theyd only be able to send a response before they observed you sending a message, but your message was already sent and received. All this would mean is that you could receive a response at the same time as they observed you sending your original message through light but it wouldnt break anything. Thinking it would break anything is like thinking the fact that you can see someone yell something at a long distance before you can hear them is time travel or breaks the rules of nature. Obviously FTL could well still be impossible no matter how advanced we get, but assuming that its impossible because you could receive information before you observed it being sent is ridiculous. It doesnt break any laws to be able to speak and interact with someone infront of you at the same time as you observe them approaching you from far away, because that person approaching from far away isnt a person, its just photons they gave off arriving after they arrived. If youre going to assume its impossible at least assume it for a sensible reason such as believing we wont ever find a method to go faster than light because it takes too much energy to accelerate mass that much, rather than falsely thinking its some kind of paradox.
@@Borg-mb8qv It's a paradox whether you assume free will or not. The entities at ABC could all be simple transistor circuits, and it would still result in a causal paradox.
If FTL is possible, then it would mean that c is not the speed of light but the speed of whatever travels FTL. We just update that and relativity stays put 😅
Imagine if you will going to Mars for three Earth years and when you get back to Earth you are three years older. Both Earth and Mars moved from day 1 to day 2 at the exact same moment in space. That would be forward motion, not time. Day 1 day 2 day 3 into Tomorrow, the future.
Woah hold your horses, the future *does* have a meaning in relativity. It's a mirror of the past: everything that can affect us is in our past, everything we can affect is in our future. It is just that these terms are smaller than in our intuition: at a distance, the past does not touch the future, instead there is a huge timeframe of causally disconnected events where you can't agree whether they are in the past, present or future based on your reference frame (we might as well call all of that "quasipresent" or just "present" if we want, baring in mind it is not a moment in time but a huge region in spacetime).
Watching your videos always allow me to discover something amazing about our world. We are fortunate to have amazing researchers like you to provide us with these hard to grasp knowledges. Thank you
6:36 If you are wondering, even a very small speed like 1 meter per second (2.24mph), the time difference would be 3 days if my calculations are correct
Oh, I love this. And the topic of the future is really timely. I have been studying the remaining portions of the writings of the pre-socratic philosopher Parmenides of Elea. Really odd stuff. He was of the belief that time was an illusion and that all past, present, and future exist simultaniously. His student was Zeno famous for Zeno's Paradoxes. It has gotten me very interested in the philisophical idea of Eternalism. The fact that even at non-relativistic speeds, different reference frames have different ordering of distant events seems to support this position. But because what is happening distantly can't actually be measured and its information sent to us any faster than light anyway, it ends up leaving the world of science and entering the world of philosophy. Thank you for this video. So good.
My god I have been in love with your channel , I’m stuck in my paradox I don’t want your channel to become super huge but at the same time you deserve all the praise ❤❤
Fantastic explanation of the Andromeda Paradox! Apropos, the way you advertised squarespace was also great. I guess this was the first time I watched an advertisement until the end 😄.
This channel is amazing. You good sir, do an amazing job explaining to people who are not experts. Also love the vibes od the channel, super upbeat and keeps it entertaining.
This one of the greatest physics channels of all time and all reference frames ❤ . Btw mahesh you need to do some videos about quantum mechanics especially the string theory pls 🙏🙏🙏🙏🙏
@FloatHeadPhysics I looked in the comments and I can't believe that I'm the only one that caught this. Your exact words at 1:00 are "Imagine there are two stop clocks right in front of you and your goal is to start them at exactly the same time" . Then you choose a method of starting them that does NOT start them at exactly the same time from everyone's perspective.
What a great video! Loved it! When I first learnt relativity I was very puzzled by the Lorentz transformation for time, t'=gamma(t-vx/c^2). It seemed odd that it contained x. Apparently it implied the change in time depends not only on relative speed but also how far away you are. You can get a big change in time by either having a high speed or a big spatial separation. It literally took me years to realize "so what". If only I'd seen your video back in the day! There is a relativity joke in there somewhere but I can't quite grasp it :D. I wonder if I could persuade you to do a video on spacelike intervals where for some observers the effect comes before the cause?
Great one 👍 got my sub. I watched your video on causality with Einstein's slap,😶🌫️ and this video ties it together well. The sp.of light is really the speed of causality, or "the speed of information." These observers musn't worry about those cunning Aliens invading sooner than expected because the Aliens can't outrun the information that is constantly spying on them for us. 👽〰️🔭👀
This is a great video on the "relativity of simultaneity." I think a deeper issue really is what is sometimes called the "conventionality of simultaneity," which asks, how do you even define simultaneity to begin with? And yes it is related to the one-way speed of light dilemma as well. I think understanding "conventionality of simultaneity" is helpful to understanding "relativity of simultaneity."
That whole explanation fell apart when 2.5 million years passed. If the runner had been running for 2.5 million years, they wouldn't still be next to you.
Right. If she would be traveling straight into direction of aliens, the light traveling from aliens would have a shorter distance. Therefore guy sitting on a bench would see monday while she sees friday. While all those events happened long time ago and alies are extincted by now.
Wow great presentation Mahesh sir 👍🙏, actually "today is tomorrow's yesterday" 😅😅 similarly "present is future's past" and hence as per vedanta everything is relative and predetermined.
Amazing! You made my day, Mahesh, thank you. This consequence might improve our understanding of supernovae, since we typically see them in retrospect, sometime after they have brightened. But, if we were able to accelerate a space telescope toward a SN, then we could watch what happens during the core-collapse phase leading up to the explosion and see the first milliseconds of brightening. And then we could compare the collapse phase and brightening timeline to the neutrino profile, measured on Earth.
My mind hadn't been this blown by physics since learning what neutron stars were a few years ago, and I'd been missing the feeling. Thanks for bringing me back into it.
Since I was a little boy, it always made sense to me that free will is an illusion, that the nature of the Universe is deterministic. I stand by it to this day. We are nothing more than just a bunch of particles interacting with each other and all the others around us, no matter how sophisticatedly arranged, we (a bunch of particles) still have to exist and behave by the rules. Things evolve in time with an order, the math and all the unmeasurable amount of variables are just infinitely complicated for our small brains to understand them, much less predict them. Nonetheless, the illusion feels real to us and we should enjoy it and just live our daily lives not caring about it, because in the end it doesn't really matter. Be happy and just enjoy this fascinating, unforgiving and beautiful Universe.
Why can "we( a bunch of particles)" choose to walk up a hill, while all the particles by themselves would follow their world line and universal law of motion and roll down it? Don't we all behave by the same physical rules? Why the contradiction?
Just discovered your channel and am binging all your videos. You're amazing. I love you! Your enthusiasm is infectious. And when you stop and are like "wait einstein what about this" your questions are exactly the questions that I have as you're talking, your flow is so perfect for me.
I love how several branches of knowledge reach the same conclusion that life or existence is meaningless. The video suddenly got philosophical. I felt like I am watching a philosophical lecture. Love your videos !!
@FloatHeadPhysics So "in VERY short": Causality travels at the speed of light, hence talking about "now" (aka simultaneity between events) regarding something that is not absolutely sharing our point in space(time) is purely hypothetical... Because it will remain unknown until the light from the events reach us... That's at least how it appears to me "now" ;)... And thanks for another fantastically entertaining AND thought provoking AND informative video... That is quite the feat, and very much of it is due to Your personal presentation, Your apparent enthusiasm and engagement really "sells it" imho ((Of course I understand and appreciate that there is a LOT of hard work in making good approachable and easily understandable explanations to make that even possible)). And I hope You manage to keep it up, and get the well deserved recognition and success that You deserve. Best regards.
I recently read a book about an event which took place in the 1700s. A ship wrecked and a group of people survived, and eventually made it back to England, where they were from. In the time between the wreck, and the eventual return of some of the people, the people had been declared dead, the families had moved on, etc. Once new information came to light, it complicated things. It makes me think, before we had near instantaneous communication through telegraph, or eventually radio and light waves here on Earth, there wasn't even always an agreed upon, "NOW." In the same, "NOW," those people were declared dead in one part of the world, they were still struggling to survive in another.
this is the first time I hear about this paradox by name. This is also the first time I see someone trying to explain the idea of "but something must be happening NOW somewhere else!". It is a very hard concept to grasp since on earth we all basically share the same "now". Mindblowned.
you dr mahesh were my finally stepping stone into "truly" understand advanced physics like relativity and qft, truly is a big word so what i emant what understand it as much as i think is adequate because i dont think we can get those 100% down just yet
I come for the awesome science education communication. I stay for the extremely contagious positivity. Seriously i love your up beat attitude and excitement, it genuinely makes my day better every time i see one of your videos.
Hi Mahesh. I loved the video, thank you. But I have a question. At around 13:30 you point out that the jogger will claim that the light has been travelling for more than 1 second. But haven't you overlooked that the two clocks will be less than 1 light second apart (to her) because she is running? Or is this effect perhaps less significant?
Except the Lorentz factor at low speed is g = 1 + v^2/2, while clock bias goes as x*v, so you can always pick v and X so g doesn’t matter to first order.
Finally someone is talking about this simple example to explain the illusion of past/present/future. It's happening in front of our eyes but hardly anyone use this as an example. There can't be a better example than night sky. It's so simple yet so fascinating. Thank You.
I learned all this from books in the 90’s. Now it is so easy to get this information. I still think it’s worth reading, but using videos like this to supplement is an amazing gift to young scientists or just anyone.
This is a good argument against the possibility of FTL communication. It would be easy to set up a real paradox if you could talk to those aliens in Andromeda in real-time.
Thanks for these videos! Quick question tho. 2:16 “motion is relative” hence the speed, correct? Then knowing the other postulate that “speed of light stays the same if all reference frames” means that light have no speed, otherwise it would be different depending on the reference point, right?
Tough to completly understand, but was still fun the parts o got. I wonder if it would be worthwhile getting into the perspective of the aliens on their frames of refrence.
What about a supernova explosion in the Andromeda Galaxy that is visible here? So the jogger saw the explosion days before the benchsitter does? She can remark to the benchsitter that she saw an event before it’s happened in his perspective?
I am feeling proud that there are still some teachers in India who rather than just following very bad and wrong education style and system, changing the way to look at physics with another perspective and explaining real majic of universe with physics. One is you amd other one is Vigyan Recharge
In the beginning, when we were at rest and the girl was jogging, she saw that the second clock was slightly "older" (for a lack of a better term). But what happens when she stops as soon as she reaches our position, after the signal was sent? Prior to stopping, she saw the first clock delay because from her FoR everything was moving towards her and the light velocity remained constant, as you said. But when she stops, what does she see? Should the clocks "correct" themselves and become in sync again?
It puts her in exactly the position as the static observer. She will see both clocks in sync again, but her view of the time they display will be very slightly different from our original observer, offset by her physical distance from the original observer.
I discovered your channel two days ago, and you have become my favorite science communicator by far! Keep up the great work!
Great to hear that :) Welcome aboard :)
Exactly what happened to me. Great channel!
Sir Thoda Hindi mein bhi bola Karo kabhi kabhi samajh nahi aata hai@@Mahesh_Shenoy
Same
Ditto. This channel is soooo intuitive, and profound. Every. Single. Episode.
Physicist Carlo Rovelli has a nice short book called "Order of Time" where he explains this quite vividly. Basically "now" is only applicable to "here" and we intuitively extend it to things around, and that kind of works while discrepancies remain too small to notice. But on a larger scale "now" doesn't mean what we're used to, it loses its meaning. All the region of spacetime outside our past and future light cones is "extended present" with no fixed order "before or after or now" relative to us, and it's not directly observable anyway. He offers some casual metaphors from real life to get accustomed to such thinking.
Thanks for the recommendation :)
@@Mahesh_Shenoy How do you know that we don't see Andromeda galaxy as it is right now? Relativity of simultaneity means you cannot agree on what is right now outside your reference frame therefore you cannot claim that light takes time to travel towards you because that is only under the assumption that light travel at speed of light in every direction. The truth is two way speed of light is constant but the light could travel one way at any speed between c/2 and infinity.
@@classicalmechanic8914that's why Einstein already mentioned in his original 1905 paper about light Speed. He said that "all the theory is made under the speculation about TWO WAY LIGHT SPEED is 'c'. We never know one way light speed. So one way light speed can be even infinite, but there is no way to test it. So we kind of belive it that it is c/2. Because we can't even test it or prove it nor disprove it.
And nobody knows what the spacelike 'extended present' outside of our light cone means. It is interesting, as this is where inflation and all cosmic theories come in, considering the cosmic background radiation is within our (past) light cone. We have no idea or even an inklinkg what this spacelike extended present could even mean.
Now that I mention this, I wonder what the implications for black holes are, where apparently time and space kind of switch, this means there is a phase transition in what it means to be an spacelike extended present. Wonder what it could tell us about it, the black hole dynamics. Considering our current universe would be the spacelike extended present for the black hole at the event horizon where time and space switch roles and flip!
@@classicalmechanic8914It should be possible to see Andromeda (thougj may not be probable) at it is in the present or by a margin of a few seconds (also taking into account delay in our consciousness of reality). That is, thru a wormhole. But if there are naturally more wormholes in the universe, well, we could have been seeing things that are much farther away than they really are, and we are there seeing a mixed of observation of the past in the present.
That was the smoothest segue of introducing a sponsor into a UA-cam video that I have ever seen.
Einstein was asked if a femtosecond is the shortest measurement of time. He answered no. The shortest measurement of time is the time between when a traffic light in New York City turns green and when the driver of the car behind you beeps his horn.
I hate it, but I respect it.
New Delhi drivers honk in negative time.
It is astounding how you've managed to clear up EVERY single follow up question i had after watching your earlier videos (coming in from the triplet paradox video).
In three videos you have cleared up questions I've had unanswered for years.
You should be required viewing in every science class in every school, anywhere. This is a level of teaching excellence that I've not only never seen before, but never even thought possible.
If the universe is moving forward and you move forward with the universe, did you really move forward yourself? If I were on Mars at 9 o:clock what time would it be here on Earth? It wouldn't relate. The orbit of Mars is not equal to the orbit of Earth so the hours in the day would not even be close. If 1 day of Earth was 3 months of Mars how much older would I be when I get to mars and do I age the same as if I were on Earth? I would age the exact same on either planet of Galaxy. We are moving forward with the universe.
This video is some truth and a lot of rubbish. Ppl love to talk like they know about things they just don’t know. There’s sooooo much we just don’t know or understand. Keep seeking TRUTH. Only Our Creator actually knows what’s up. Seek Him. 🙏
@@queenj.8i895 It's funny you talk about the "truth" and then say only the "Creator" knows
Mahesh, all the hard work in the animations and the smooth delivery of explanations are revolutionary and all, but deep down you know you've turned pro when you've seamlessly segue into the sponsor spot without any transition. Achievement unlocked!
Einstein says he is proud. It's ok if you didn't hear it, he was in another frame 😉
It's ok, he will hear about it in about 1 or 2 million years.
To address the very last question in the video
You explain it very well and ill put it in different words:
Someone once explained it to me in a very simple way - each observer: me, the jogger and the aliens in Andromeda have their own time. Imagine it like a track, and the word "now" is a point on that track. Since every one has their own track, the word "now" is personal. Ie each person's now will refer to a point along his own tracks - there is no necessity to be able to map each point on your tracks to some point on another's (arbitrary) tracks. They are simply just different tracks, and each observer has chosen a different path through spacetime. You dont have to be able to link these tracks together, why would you?
If you want to try to make "objective" sense of the situation than it would seem as if you would have to try and link them together.
@@TheKingWhoWins which can only be done meaningfully if they meet again
so it's meaningless to track the meteor until it hits us?
@@MadsterV no it's meaningless to speak about its time in a way that maps points on its time to ours unless that meteor is local which it will be long before it hits us. It's like hearing someone say "the *local* speed of light is c" and then saying "oh so the speed of light isn't constant, they lied to us"
And anyway - the meteor hitting us is an absolute truth, it either hits us or doesn't. So we can use *our* time to track it - nobody is forcing us to link our time to the meteor's time. And anyway (again) if we want to predict what state it will be in by the time it hits us (eg idk, perhaps what percentage of its radioactive isotopes will have undergone fission), yes we can use its own time - again, linking it to ours is unnecessary for this calculation
Ok. dude turned a commercial for website building into an existential crisis.
Ikr.... very cool
😂
It is all a lie. Time is not relevant to anything other than Earth.
I'm taking a bunch of classes right now online, in unrelated subjects, and I just want all of those instructors to watch your videos. A good teacher makes such a difference!
This guy is brilliant.
Andromeda is not just separated from us in space but also equally in time. Just as we can not reach Andromeda in space, we can not reach it in time. We're essentially de-synced in time by 2.5 million years. If we were to travel to Andromeda, that desync in time would shrink as the distance between us shrank. So when we arrive somewhere we don't just arrive there in space, but also in time. Hence the term, spacetime. With that in mind, the "present" is only local to you, and the further something is from you the more in the past it is from you as well.
That's a great point. Weirdly, our human brains deals as "there is an universal clock, now is happening everywhere, and when we see the stars, the light travelling to us gives an illusion that something is happening right now"
But it's false. It's not an illusion. The real "now" is the speed of light. "Seeing the past" is not an illusion, is the real "now" for you locally
Which would make it really cool to watch it as we traveled toward it to see what happens all the way up to the point where we reach it and see it as it is at that point.
Very interesting
unfortunately your statement, however clever, is still not quite right. it assumes there's an absolute set of 4 dimensional coordinates, three spatial and one time, but that's not quite the case. in reality, we have local sets of 4 dimensional coordinates (our frames of reference) but their relation to other frames of reference change as a function of of many dynamic variables, it's not as simple as setting a desired point in 4-dimensional world and then saying we'll meet there, the "there" changes as the world and you evolve
No. If you could hop in a wormhole you’d be at andromeda now. Yes what we see now is them 2.5 million years ago. But it does exist in the now. We just can’t see it now cause its light is taking time to get here.
What a superb channel!! Such a wonderful and engaging way of explaining these concepts. I love it ♥
Never had i seen such a natural integration of an ad . Very nice job Mahesh!
This is why it's good to play with simulators that use a speed of light much slower than normal, so one can develop a better feel for how "now" is relative.
Speed has nothing to do with forward motion. You can go forward at 1 mph. Everything inside of you is only going 1 mph. Nothing inside of you will go faster or slower than you are.
This is the first video that's convinced me that faster-than-light travel is impossible, as it would create causal paradoxes:
Lets say we have three FTL communicators, two nearby (B & C), and one in Andromeda (A). Lets say B and C are nearby, but C is jogging. B says to A "tell C to tell me to say 42", then A tells C that, but C will hear that message days before B sent it, so can tell B not to send any message at all, creating a paradox.
It's only a paradox if you assume free will 😊
That’s not how it works, C will hear the message days before they would be able to observe B sending it but C’s observation of B sending it is irrelevant to affecting wether or not B did send it
I swear these misunderstandings are only possible because we’re taught a very self centred version of time. Going faster than the speed of light is not time travel otherwise we already have that with sound you can just go further away faster than the speed of sound and hear what happened earlier than your previous observation but if you were going slower than the speed of light you won’t be seeing before your previous observation.
Only difference in your example is now light is the one coming in second place.
Edit: I said the same thing twice
I never understood why people believe that faster than light is impossible because otherwise you could get a message before you observe someone sending it... Or that you could meet an alien before you saw them leave their home planet or whatever else.
Like none of that means FTL is impossible and isnt at all odd to think about even, nor is it timetravel.
Just because you travel say 2c doesnt mean you can affect the past by sending a message somewhere and them being able to send a response before you sent your message. Theyd only be able to send a response before they observed you sending a message, but your message was already sent and received. All this would mean is that you could receive a response at the same time as they observed you sending your original message through light but it wouldnt break anything. Thinking it would break anything is like thinking the fact that you can see someone yell something at a long distance before you can hear them is time travel or breaks the rules of nature.
Obviously FTL could well still be impossible no matter how advanced we get, but assuming that its impossible because you could receive information before you observed it being sent is ridiculous. It doesnt break any laws to be able to speak and interact with someone infront of you at the same time as you observe them approaching you from far away, because that person approaching from far away isnt a person, its just photons they gave off arriving after they arrived. If youre going to assume its impossible at least assume it for a sensible reason such as believing we wont ever find a method to go faster than light because it takes too much energy to accelerate mass that much, rather than falsely thinking its some kind of paradox.
@@Borg-mb8qv It's a paradox whether you assume free will or not. The entities at ABC could all be simple transistor circuits, and it would still result in a causal paradox.
If FTL is possible, then it would mean that c is not the speed of light but the speed of whatever travels FTL. We just update that and relativity stays put 😅
This is most special channel about special relativity!
You always ask and answer the questions I have after watching other videos. Love it! Keep up the good work.
The clocks at the start not having a 9 is hurting my soul
And they have no zero either, so they are already one second in the future before they start.
Omg! I was sleep deprived. 😅
Imagine if you will going to Mars for three Earth years and when you get back to Earth you are three years older. Both Earth and Mars moved from day 1 to day 2 at the exact same moment in space. That would be forward motion, not time. Day 1 day 2 day 3 into Tomorrow, the future.
The Andromeda Paradox exemplifies that all of physics happens along time-like curves.
You are one of the best educators on Relativity out there today.
Once again our brother is back with his conversations with Einstein.
This guy is making physics way simpler for me
Wow. The way you integrated Squarespace was amazing!
Smooth af
Woah hold your horses, the future *does* have a meaning in relativity. It's a mirror of the past: everything that can affect us is in our past, everything we can affect is in our future. It is just that these terms are smaller than in our intuition: at a distance, the past does not touch the future, instead there is a huge timeframe of causally disconnected events where you can't agree whether they are in the past, present or future based on your reference frame (we might as well call all of that "quasipresent" or just "present" if we want, baring in mind it is not a moment in time but a huge region in spacetime).
I was jogging last week and totally knew that smooth squarespace segue was/is/will coming up.
Watching your videos always allow me to discover something amazing about our world. We are fortunate to have amazing researchers like you to provide us with these hard to grasp knowledges. Thank you
6:36 If you are wondering, even a very small speed like 1 meter per second (2.24mph), the time difference would be 3 days if my calculations are correct
i don't know mate you are using freedom units
Oh, I love this. And the topic of the future is really timely.
I have been studying the remaining portions of the writings of the pre-socratic philosopher Parmenides of Elea. Really odd stuff. He was of the belief that time was an illusion and that all past, present, and future exist simultaniously. His student was Zeno famous for Zeno's Paradoxes. It has gotten me very interested in the philisophical idea of Eternalism.
The fact that even at non-relativistic speeds, different reference frames have different ordering of distant events seems to support this position. But because what is happening distantly can't actually be measured and its information sent to us any faster than light anyway, it ends up leaving the world of science and entering the world of philosophy.
Thank you for this video. So good.
Sir, Please keep sending us more of your Photons and Phonons recorded from non existing now to the Future
Ah ys
My god I have been in love with your channel , I’m stuck in my paradox I don’t want your channel to become super huge but at the same time you deserve all the praise ❤❤
I don't know why, but my favorite aspect of these videos is the Socratic setup between him and Einstein. I love when Einstein goes: "BUT MAHESH!"
Fantastic explanation of the Andromeda Paradox! Apropos, the way you advertised squarespace was also great. I guess this was the first time I watched an advertisement until the end 😄.
8:46 this gave me goosebumps
I see this at 8:47 means I'm more fatigued at this moment 🥴
This channel is amazing. You good sir, do an amazing job explaining to people who are not experts. Also love the vibes od the channel, super upbeat and keeps it entertaining.
thanks for messing with my head again
got something new to think about for the next week
great vid!!
I'm watching and at 5:33 I understood where we're going. I love these aha-moments. Great video!
This one of the greatest physics channels of all time and all reference frames ❤ . Btw mahesh you need to do some videos about quantum mechanics especially the string theory pls 🙏🙏🙏🙏🙏
@FloatHeadPhysics I looked in the comments and I can't believe that I'm the only one that caught this. Your exact words at 1:00 are "Imagine there are two stop clocks right in front of you and your goal is to start them at exactly the same time" . Then you choose a method of starting them that does NOT start them at exactly the same time from everyone's perspective.
What a great video! Loved it! When I first learnt relativity I was very puzzled by the Lorentz transformation for time, t'=gamma(t-vx/c^2). It seemed odd that it contained x. Apparently it implied the change in time depends not only on relative speed but also how far away you are. You can get a big change in time by either having a high speed or a big spatial separation. It literally took me years to realize "so what". If only I'd seen your video back in the day! There is a relativity joke in there somewhere but I can't quite grasp it :D. I wonder if I could persuade you to do a video on spacelike intervals where for some observers the effect comes before the cause?
Wow the seamlessness of the ads, now THAT is brilliant! ❤️❤️❤️
Great!
Please do a video on gravitational time dilation as well and also videos on general relativity.
Yup, I have a few more to cover in special relativity, then I ll move to general relativity:)
Great one 👍 got my sub. I watched your video on causality with Einstein's slap,😶🌫️ and this video ties it together well. The sp.of light is really the speed of causality, or "the speed of information." These observers musn't worry about those cunning Aliens invading sooner than expected because the Aliens can't outrun the information that is constantly spying on them for us. 👽〰️🔭👀
This is a great video on the "relativity of simultaneity." I think a deeper issue really is what is sometimes called the "conventionality of simultaneity," which asks, how do you even define simultaneity to begin with? And yes it is related to the one-way speed of light dilemma as well.
I think understanding "conventionality of simultaneity" is helpful to understanding "relativity of simultaneity."
This was really fun. And I love your energy!
However, this means that any long-distance teleportation becomes an ideal time machine. As is FTL communication or FTL drive.
But then the question arises that how can we make teleportation possible even in the first place
4head thread
Passionate curiosity and complex concepts elucidated with simple stories. Amazing channel!
That whole explanation fell apart when 2.5 million years passed. If the runner had been running for 2.5 million years, they wouldn't still be next to you.
Right. If she would be traveling straight into direction of aliens, the light traveling from aliens would have a shorter distance. Therefore guy sitting on a bench would see monday while she sees friday. While all those events happened long time ago and alies are extincted by now.
Hey just discovered your channel like 1 month ago.
I like how you explain things.
I understand certain things about sciences much better now. Thnx
Wow great presentation Mahesh sir 👍🙏, actually "today is tomorrow's yesterday" 😅😅 similarly "present is future's past" and hence as per vedanta everything is relative and predetermined.
Amazing! You made my day, Mahesh, thank you.
This consequence might improve our understanding of supernovae, since we typically see them in retrospect, sometime after they have brightened. But, if we were able to accelerate a space telescope toward a SN, then we could watch what happens during the core-collapse phase leading up to the explosion and see the first milliseconds of brightening. And then we could compare the collapse phase and brightening timeline to the neutrino profile, measured on Earth.
There's no such thing as "now". Every time "now" occurs, it's already "then".
Could you explain this?
So deep bro
Love your uploads, you were born to do this 😊
Sir please make videos in physics in khan academy too why do you stop making videos btw I love your teaching skills sir 🥰
My mind hadn't been this blown by physics since learning what neutron stars were a few years ago, and I'd been missing the feeling. Thanks for bringing me back into it.
Since I was a little boy, it always made sense to me that free will is an illusion, that the nature of the Universe is deterministic. I stand by it to this day. We are nothing more than just a bunch of particles interacting with each other and all the others around us, no matter how sophisticatedly arranged, we (a bunch of particles) still have to exist and behave by the rules. Things evolve in time with an order, the math and all the unmeasurable amount of variables are just infinitely complicated for our small brains to understand them, much less predict them.
Nonetheless, the illusion feels real to us and we should enjoy it and just live our daily lives not caring about it, because in the end it doesn't really matter. Be happy and just enjoy this fascinating, unforgiving and beautiful Universe.
Why can "we( a bunch of particles)" choose to walk up a hill, while all the particles by themselves would follow their world line and universal law of motion and roll down it? Don't we all behave by the same physical rules? Why the contradiction?
I say we have free will, but we are slaves. Slaves with free will. What are your thoughts?
Just discovered your channel and am binging all your videos. You're amazing. I love you! Your enthusiasm is infectious. And when you stop and are like "wait einstein what about this" your questions are exactly the questions that I have as you're talking, your flow is so perfect for me.
Fantastic explanation. New favorite physics channel.
absolutely loving this content! thank you
Thanks mahesh! This is enlightening.
I love how several branches of knowledge reach the same conclusion that life or existence is meaningless. The video suddenly got philosophical. I felt like I am watching a philosophical lecture.
Love your videos !!
This is just so damn awesome, I"m going to write an article about this for my physics page inspired by your awesome explanation.
Awesome video, thanks. You’re a great communicator
Thanks :)
Happy to see you back sir.
Expecting you to appear on screen frequently instead of from time to time.
Depends on your relative motion to Mahesh.
Love the way you tied in determination and the promo for squarespace...
Gotta give props to the jogger she so motivated 😂
Love your videos
I love your content! It puts my 🧠 to work.
this is my new favorite physics channel
@FloatHeadPhysics
So "in VERY short": Causality travels at the speed of light, hence talking about "now" (aka simultaneity between events) regarding something that is not absolutely sharing our point in space(time) is purely hypothetical... Because it will remain unknown until the light from the events reach us...
That's at least how it appears to me "now" ;)...
And thanks for another fantastically entertaining AND thought provoking AND informative video... That is quite the feat, and very much of it is due to Your personal presentation, Your apparent enthusiasm and engagement really "sells it" imho
((Of course I understand and appreciate that there is a LOT of hard work in making good approachable and easily understandable explanations to make that even possible)).
And I hope You manage to keep it up, and get the well deserved recognition and success that You deserve.
Best regards.
I recently read a book about an event which took place in the 1700s. A ship wrecked and a group of people survived, and eventually made it back to England, where they were from. In the time between the wreck, and the eventual return of some of the people, the people had been declared dead, the families had moved on, etc. Once new information came to light, it complicated things. It makes me think, before we had near instantaneous communication through telegraph, or eventually radio and light waves here on Earth, there wasn't even always an agreed upon, "NOW." In the same, "NOW," those people were declared dead in one part of the world, they were still struggling to survive in another.
Subscribed. Incredible way of thinking about so many ideas. 👍👍
I love your t-shirts man 😭❤
I understood relatively perfectly for the first time. Thank you
Awesome videos man. No flux given!
"Right Einstein!? WHAT IS GOING ON!!!?!?!?!?" is relatable as hell
this is the first time I hear about this paradox by name. This is also the first time I see someone trying to explain the idea of "but something must be happening NOW somewhere else!". It is a very hard concept to grasp since on earth we all basically share the same "now". Mindblowned.
you dr mahesh were my finally stepping stone into "truly" understand advanced physics like relativity and qft, truly is a big word so what i emant what understand it as much as i think is adequate because i dont think we can get those 100% down just yet
Best job of working your sponsor into the content I've ever seen.
"The distinction between the past, present and future is only a stubbornly persistent illusion" -- Albert Einstein, 1922.
I come for the awesome science education communication. I stay for the extremely contagious positivity. Seriously i love your up beat attitude and excitement, it genuinely makes my day better every time i see one of your videos.
Hi Mahesh. I loved the video, thank you. But I have a question. At around 13:30 you point out that the jogger will claim that the light has been travelling for more than 1 second. But haven't you overlooked that the two clocks will be less than 1 light second apart (to her) because she is running? Or is this effect perhaps less significant?
Good catch 🙆
The distance would be length contracted. But, it still works out to be more than 1 second!
@@Mahesh_Shenoy Thanks!
Except the Lorentz factor at low speed is g = 1 + v^2/2, while clock bias goes as x*v, so you can always pick v and X so g doesn’t matter to first order.
@@DrDeuteron Yes, I came to a similar conclusion once I took a little more time to think about it.
0:16 this man is gonna end Vsauce's whole career
Great presentation, I've subbed.
Free will is indeed an illusion.
Loved this one
Bravo, bravo, bravo, to you! You made this so easy to understand. Thank you!
Finally someone is talking about this simple example to explain the illusion of past/present/future. It's happening in front of our eyes but hardly anyone use this as an example.
There can't be a better example than night sky. It's so simple yet so fascinating. Thank You.
Loved this guy's tshirt collection...
Love your t-shirt 🔥
I learned all this from books in the 90’s. Now it is so easy to get this information. I still think it’s worth reading, but using videos like this to supplement is an amazing gift to young scientists or just anyone.
I love the way you speak.
It's halfway to singing.
The Welsh are the same.
This is a good argument against the possibility of FTL communication. It would be easy to set up a real paradox if you could talk to those aliens in Andromeda in real-time.
You cannot “see” a radio signal like you see a clock.
Best channel for physics
I must not be the target audience because I *loved* Atlantis. RIP...
Thanks for these videos! Quick question tho. 2:16 “motion is relative” hence the speed, correct? Then knowing the other postulate that “speed of light stays the same if all reference frames” means that light have no speed, otherwise it would be different depending on the reference point, right?
My brain just exploded!
Seriously though, I’ve learned more physics in a two day binge listening to Mahesh’s videos than a semester in college.
Tough to completly understand, but was still fun the parts o got. I wonder if it would be worthwhile getting into the perspective of the aliens on their frames of refrence.
What about a supernova explosion in the Andromeda Galaxy that is visible here? So the jogger saw the explosion days before the benchsitter does? She can remark to the benchsitter that she saw an event before it’s happened in his perspective?
I am feeling proud that there are still some teachers in India who rather than just following very bad and wrong education style and system, changing the way to look at physics with another perspective and explaining real majic of universe with physics. One is you amd other one is Vigyan Recharge
Please make some videos on other topics also
In the beginning, when we were at rest and the girl was jogging, she saw that the second clock was slightly "older" (for a lack of a better term). But what happens when she stops as soon as she reaches our position, after the signal was sent? Prior to stopping, she saw the first clock delay because from her FoR everything was moving towards her and the light velocity remained constant, as you said. But when she stops, what does she see? Should the clocks "correct" themselves and become in sync again?
It puts her in exactly the position as the static observer. She will see both clocks in sync again, but her view of the time they display will be very slightly different from our original observer, offset by her physical distance from the original observer.
I love your tee shirts almost as much as I love your videos !
Surfsark India Mein Bhi Aa Gaya Kya?
Nice Video. 👍